A large body of evidence reviewed in Section IIA indicates that monoamine oxidase (MAO) exists in at least two catalytically and immunologically distinct forms. In order to better understand the biology of this pharmacologically important enzyme the following experiments are proposed: a. MAO will be purified from rat liver (a source for both enzyme forms) to the highest possible degree by using modifications of existing methods. The two forms of the enzyme (MAO A and MAO B) will be resolved by affinity chromatography with a specific inhibitor of MAO A as a ligand. b. Once the enzyme forms have been resolved, the subunit structure of each MAO A and MAO B will be analyzed by disc gel electrophoresis in the presence of denaturants (e.g., sodium dodecyl sulfate). Sufficient amounts of each subunit will be prepared electrophoretically to use as a pure antigen. Particular attention will be directed towards the subunit bearing the covalent flavin. c. Using each subunit as an antigen, monospecific antibodies will be prepared and these antibodies will be used to evaluate the relationship of the subunit structure of these enzyme forms and their catalytic differences. d. The antibodies will also be used as reagents to determine the hepatic site of biosynthesis of MAO A and MAO B (membrane bound ribosomes, free ribosomes or mitochondria) with respect to the apoprotein and the flavin cofactor. Using radioactive amino acids and riboflavin, the turnover rate of each form will be estimated. e. The monospecific antibodies will also be used in conjunction with fluorescent antibodies to determine the anatomical localization of these enzyme forms in the rat brain. It is expected that the completion of the proposed experiments would not only contribute to an understanding of the biology of this enzyme but would also provide data relevant to the interpretation of pharmacological data obtained with MAO inhibitors and be of importance in understanding some aspects of diseases bearing a relationship to MAO (mental depressions and hypertension).